1. Field of the Invention
The invention relates to a welding construction for an electrically conductive plate to arc-weld a lead portion of a device, such as an electric or electronic device, and a welding method using the same.
2. Description of the Related Art
An electronic device used in a circuit of an electrical part generally has a lead for connection with an electrically conductive plate, such as a busbar, of the circuit. This connection conventionally has been made by welding connection points of the lead and the plate. More particularly, the lead of the electronic device and the electrically conductive plate are connected electrically by melting a part of the electrically conductive plate to coat the leading portion and fixing the lead to the electrically conductive plate.
U.S. Pat. No. 5,541,365 discloses a beam-weldable terminal construction of an electrically conductive plate that is suitable for welding as described above.
FIGS. 7A and 7B are perspective views showing a known beam-weldable terminal 1 with a part thereof left out, wherein FIG. 7(A) shows a state before welding and FIG. 7(B) shows a state after welding.
With reference to FIG. 7(A), the beam-weldable terminal 1 includes a bottom wall 2 and two holding walls 3 that extend from the opposite lateral sides of the bottom wall 2. A wire accommodating portion 5 is defined by the bottom wall 2 and the holding walls 3 for accommodating a wire 4. The depth from the upper surface of the bottom wall 2 to the upper edges of the holding walls 3 of the wire accommodating portion 5 substantially equals the diameter of the wire 4. Thus, the wire 4 can be held tightly between the holding walls 3 and placed on the bottom wall 2 without being exposed upward. A projection 3a extends up from the upper edge of one holding wall 3 and is narrower than the holding wall 3. The wire 4 is accommodated in the wire accommodating portion 5 of the beam-weldable terminal 1, and a laser beam is projected onto the bottom of the projecting portion 3a as indicated by an arrow Y1.
With reference to FIG. 7(B), the laser beam creates heat energy at a touching portion between the wire 4 and the holding wall 3. Thus, a coupling portion of the projection 3a and the holding wall 3 and a portion near it are melted. As a result, the projection 3a deforms toward the wire 4 and melts to coat the wire 4. The beam-weldable terminal 1 and the wire 4 are connected electrically by coating the wire 4 with the projection 3a, and the projection 3a subsequently solidifies. Thus, the solidified projection 3a fixes the wire 4 to the beam-weldable terminal 1.
A laser welding machine is required to project a laser beam onto the welding point to weld the lead and the electrically conductive plate of the beam-weldable terminal 1 to each other. The laser welding machine of this type is very expensive. Additionally, many kinds of welding steps often must be performed in parallel, and it is necessary to prepare the laser welding machine for each welding step. This leads to a huge investment in equipment. Therefore, there has been a demand to connect an electronic device and an electrically conductive plate by arc-welding using a less expensive arc welding machine.
An arc welding machine can melt an electrically conductive plate by bringing an electrode of the arc welding machine close to the electrically conductive plate that is to be welded. Arcs are created between the electrically conductive plate and the electrode and the arcs produce heat energy in the electrically conductive plate. The electronic device and the electrically conductive plate are connected by melting the electrically conductive plate in this way.
FIG. 8 illustrates a problem that occurs when attempting to connect the aforementioned beam-weldable terminal 1 and the wire 4 by arc welding. In particular, arcs created from the electrode of the arc welding machine tend to be directed toward closer parts of the electrically conductive plate, unlike the aforementioned laser beam. Thus, even if an attempt is made to create arcs at a position indicated by the arrow Y1 in FIG. 7(A), the arcs may be created at irregular positions of the beam-weldable terminal 1.
For example, arcs may be created at the upper ends of the projection 3a as indicated by arrows Y2, Y3. In such a case, the projection 3a melted by the arcs may deform toward a side opposite from the wire 4 and outside of the wire accommodating portion 5. As a result, the wire 4 may not be coated and may not be connected properly with the terminal 1. Further, even if the molten projection 3a is deformed toward the wire 4, the molten state of the projection 3a and the coated state of the wire 4 differ depending on whether arcs are created as indicated by the arrow Y2 or Y3. Thus, connection strength of the terminal 1 and the wire 4 may differ.
Arcs could be created to reach the wire 4, as indicated by an arrow Y4. Thus, the projection 3a has to be melted by the transfer of the heat energy of the arcs to the terminal 1. However, the heat transfer takes time. Additionally, heat energy applied in this manner may make the connection between the terminal construction 1 and the wire 4 unstable and may damage the wire 4.
Connection of the terminal 1 and the wire 4 by arc welding is unstable and has no reproducibility. Furthermore, the wire 4 may be damaged since the arcs are created unstably at positions indicated by the arrows Y2 to Y4.
The invention was developed in view of the above problems and an object thereof is to provide a welding construction that causes arcs to be created stably at a desired position and that connects an electric or electronic device and an electrically conductive plate with reproducibility by arc welding without damaging the device and a welding method using such a welding construction.